Life cycle assessment of bioethanol production by two methods of pretreatment of rice straw based on process simulation

In the life cycle assessment of bioethanol processes under choline chloride/urea (DES-U), choline chloride/lactic acid (DES-LA) and sodium hydroxide (NaOH) pretreatment studied. As the net energy values under DES-U, DESLA pretreatment was negative, which were - 4,107,023 MJ and - 643,449 MJ, respectively; they could not get positive energy benefits. High solid loading pretreatment could directly reduce the total net energy input. The net energy ratios of DES-U and DES-LA were 0.00644, which were much lower than 1.01 of NaOH. The renewability of DES-U and DES-LA were 0.0412 and 0.0414, respectively, which were much lower than NaOH (1.24). Renewability under three pretreatments was increased in the cases of predominantly lignin-rich residue supply. The coal consumption of DES pretreatment was more than 1.93 times NaOH, resulting in high CO2 emission. The coefficients for greenhouse gas emissions (GHG), ozone depletion and fossil depletion of three pretreatments were less than 1 %, with high confidence. For NaOH, DES-U, DES-LA, the GHG emissions were assessed to be 10,278.8, 12,801.8 and 8528.3 kg CO2 eq., respectively. When lignin residue instead of coal was used as energy supply raw material, GHG emission of NaOH, DES-U, DES-LA processes decreased insignificantly, which reduction were 33.3 %, 33.4 % and 28.4 % for kg CO2eq.